A report for the UN Human Rights Council cites growing evidence that Western-made bombs are being used in potential war crimes in the conflict.

Britain and US supply Saudi Arabia with munitions that are used in Yemen. A US laser-guided bomb is believed to have been used in a strike this month that killed 40 children.

At least 6475 civilians have been killed since the Saudi intervention in Yemen began in March 2015 but the report warns that the real figure is likely to be "significantly higher".

Most of the civilians were killed by airstrikes carried out by the Saudi-led military coalition. The report noted that strikes have hit "markets, funerals, weddings, detention facilities, civilian boats and even medical facilities".

Human rights groups repeated their calls for an end to arms sales.

"Our allies Saudi Arabia and UAE are among the parties accused of potential war crimes, and yet the UK continues to sell weapons to both," said George Graham, Save the Children's director of conflict and humanitarian advocacy.

A British Foreign Office spokeswoman said the Government was "carefully considering" the UN report.

The Saudi-led coalition said it had referred the report to its legal team.

James Mattis, the US Defence Secretary, said US support for the coalition was "not unconditional" but gave no indication that the US planned to withdraw support.

"Our conduct there is to try to keep the human cost of innocents being killed accidentally to the absolute minimum," he said.